Laurence Holmes-

(CBS) Mystery solved. Brian Urlacher had arthroscopic surgery Tuesday morning on his left knee.

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The Bears said the procedure was done to “relieve the swelling” that Urlacher had been suffering from for the last couple of weeks. From all accounts, this wasn’t a repair on Urlachers’ MCL/PCL. The team still believes he will be on the field for the opener against Indianapolis on September 9, but that remains to be seen.

The usual recovery time after a non-invasive procedure like this is 6-8 weeks, depending on the depth of damage of the knee. Bears surgeons Gordon Nuber & Mark Brown handled the surgery. If the fraying of cartilage wasn’t too severe, Urlacher could be back before that. A medical expert that I talked to said 6-8 weeks is normal, but in this situation there could be some wiggle room built in. So, it’s not out of the question that he could be on track to play against the Colts, but that also means that he may be playing with some residual swelling and irritation.

NFL scheduling wasn’t kind to the Bears or Urlacher’s recovery. The Bears play the first the Thursday night game of the year, the following week in Green Bay. That doesn’t allow for a lot of recovery time. Urlacher has only participated in a few practices and it seems unlikely that he’ll get any game-time reps before the opener to truly test how his knee will respond.

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Urlacher has missed most of the practices in Bourbonnais and the preseason opener against Denver. Nick Roach has been taking all of the first teams reps with Lance Briggs staying at his usual weak-side spot and offseason acquisition Geno Hayes playing strong-side (where Roach usually is). Roach is a competent NFL linebacker, but this defense was designed for Uralcher’s skill set. His ability to cover the deep middle of the field is a significant difference between the “Tampa-2” and the “Bears-2”.

Considering the late date of the surgery, it leads you to wonder if this injury will linger and what effect that will have on the Bears. If Urlacher’s recovery doesn’t go well and he’s forced to miss some time, it could leave a big void in the defense.

“His value is everything.” Charles Tillman told the Score on Monday. “We saw how valuable he was when he missed the entire 2009 season. It’s like playing with a coach on the field. It’s like having Lovie next to you.”

The Bears have Superbowl aspirations. Having a healthy Urlacher is a big part of the reason, the team feels so confident coming into the year. The Bears are hoping and saying publicly that they expect Urlacher back. They’ll take the tradeoff of age and injury diminishing him vs. not having him at all.

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“His value to us is priceless. He’s the defensive verison of Peyton Manning.” Tillman said.